Wet diaphragm electrostatic printer



April 6, 1966 R. B. JOHNSON WET DIAPHRAGM ELECTROSTATIC PRINTER FiledApril 23, 1963 LATENT IMAGE FORMING MEANS POLARIZED INK APPLIGATOR FIG.

' IG INPUT IMAGE FORMATION mi i.

INVENTOR. REYNOLD B. JOHNSON BY 91., My

I/ ZO DIRECT CURRENT v VOLTAGE SUPPLY CONTROL UNIT FIG.3

ATTORNEY United States Patent 3 247,825 WET DIAlhRAGM ELECTROSTATKCPRTNTER Reynold B. Johnson, Palo Alto, Calif, assignor to InternationalBusiness Machines Corporation, New York, N.Y., a corporation of New YorkFiled Apr. 23, 1963, Ser. No. 275,071

9 Claims. ((31. 118-637) This invention relates to electrostaticprinters in general and more particularly to an electrostatic printerwherein electrostatically attractable ink is deposited on one side of athin porous sheet member and an electro static pattern deposited on theother side thereof to selectively draw ink through the porous member fortransfer purposes.

In most electrostatic printers is use today, a latent electrostaticimage is formed by conventional means on an insulator member. Theelectrostatic image is then dusted with an electroscopic powder known astoner which is attracted to the latent electrostatic image to form avisible image of the charge pattern. The thus toned image is thentransferred to a paper or other similar output member. The toner is thenheat-fixed or solvent-fixed to the paper to provide the final image.

Problems attendant present day systems which utilize toner for adeveloper are that large black areas in an image are usually notuniformly developed; instead, there is a heavy concentration of tonerparticles at the outer edge of the large black area with a much lesserconcentration of toner particles in the inner portions of the area.Additionally, the toner is quite messy and hard to handle and the fixingoperation slows down to a considerable extent the throughput of thesystem.

Attempts to devise a system wherein the developer is not a microscopicpowder to thereby provide a system capable of producing large blackareas satisfactorily and which does not require the fixing operation,have resulted in a liquid development type of system. Liquid developmenttype systems have proved satisfactory in most applications, but incertain applications such as where the electrostatic image is formed,not through use of conventional photoconductor techniques, but isformed, for instance, by the selective energization of electrostaticprobes or pins disposed adjacent the insulator belt, as in the case ofcomputer output printers, terminal or facsimile printers, airborneprinters, etc., certain shortcomings have arisen. For example, oneelectrostatic printer in use today employs electrostatic probes whichare disposed on one side of a paper web wihch is to be printed on and anink source disposed on the other side of the paper web. The probes areselectively energized and the electrostatic attraction provided therebypulls ink from the ink supply onto the print medium to form images. Thissystem is quite limited in speed of operation due to the relatively slowresponse of the ink to the electrostatic charge.

An object of the present invention is to provide a novel electrostaticprinter employing a liquid development technique.

Another object of the present invention is to provide a relatively highspeed probe-type development electrostatic printer.

Another object of the present invention is to provide an electrostaticprinter wherein liquid development techniques are used without resultanthigh background printouts.

Other and further objects and advantages of the invention will beapparent from the following more particular description of the preferredembodiment of the invention, as illustrated in the accompanying drawingin which:

Patented Apr. 26, 1966 herein disclosed novel electrostatic printingsystem;

FIG. 2 is an isometric view of the preferred embodiment of the hereindescribed electrostatic printer; and

FIG. 3 is a sectional View of the insulating belt utilized in theelectrostatic printing system described herein.

Briefly, in the preferred embodiment, input information forms anelectrostatic image on the surface of an endless belt made of thin,insulating plastic material, such as Teflon. The belt is perforated withmany small, closely spaced holes. An inking roller applys ink to theunderside of the perforated plastic belt. The latent electrostatic imageis formed on the upper surface of the belt by means of a high DC.potential selectively applied across charging wires and the inkingroller beneath the belt. Since the belt contains numerous small holes,the polarized molecules of ink on the underside are attracted by chargesof opposite sign forming the latent image on the upper surface of thebelt. Consequently, ink Will be pulled upward through the holes inaccordance with the charge pattern of the latent electrostatic image. Bythe time the belt reaches an associated print station, sufiicient inkwill have been pulled up through the holes so that full characters canbe transferred to a paper web which is brought into pressure contactwith the upper side of the belt.

For a more detailed description, refer first to FIG. 1. In FIG. 1 isshown a thin porous belt 1 made of an insulator such as Teflon beingmoved in the direction of the arrow 2 by suitable means (not shown) pasta latent image forming means 3 and a polarized ink applicator 4. Theinsulator belt 1 then passes in rolling contact with a paper web orother similar print member 5 which is moved in the direction of thearrow 6. The paper web 5 is pressed by means of roller '7 into rollingcontact with the belt 1.

As better shown in FIG. 3, the insulator belt is porous, having formedtherethrough numerous tiny holes 9. While for simplicity of drawing, theinsulator belt of FIG. 3 is illustrated as having cylindrical openingsor holes formed therethrough, commercially available materials suitablefor use in the subject application are more spounge-like in makeup.

In operation, a latent image 10 is formed by means of the latent imageforming means 3 on the upper surface of the insulator belt 1. Any ofseveral latent image forming means may be utilized. For instance, as inthe preferred embodiment of the invention, a head having selectivelyenergizable electrostatic probes may be utilized as the latent imageforming means 3. Another type of latent image forming means which may beutilized in the subject invention is the photoconductor type wherein thephotoconductor is charged in darkness to a uniform potential. An imageis then projected onto the charged photoconductor to form a latentelectrostatic image. This latent electrostatic image may then betransferred to the belt 1.

Polarized ink is supplied by means of the polarized ink applicator 4 tothe opposite or under surface of the belt 1. The polarized ink may beapplied to the underside.

of the belt 11 through use of a roller as in the preferred embodiment orby any other suitable means. The sequence of application of the latentimage ill to the belt and the application of the ink to the oppositesurface of the belt need not necessarily be in the order as depicted inFIG. 1. Instead, the ink may be applied to the under surface of the beltprior to or simultaneously with the application of the latent image tothe upper surface of the belt 1.

As the belt 1 travels toward the contact station which comprises roller7, ink is drawn through the small holes from the underside of the belt 1by the latent image 10 on the upper surface of the belt such that by thetime that the portion of the belt bearing the latent image reachesroller 7, an ink image 11 will have been formed on the upper surface ofthe belt 1 in the configuration of the electrostatic pattern 111. Theink image 11 then passes in rolling contact with the paper web 5 thustransferring it to the paper .web.

With respect to the belt 1, any of several types of insulators may beutilized. It has been found, however, that the laws of capillarity maywork against clean printing such that ink may seep through all of theholes of the porous sheet and print out as a heavy background whenWettable insulators are used. Thus, Teflon, which is relativelynon-wettable, has been found to be a good insulator belt material.Likewise, any of several types of electrostatically attractable ink maybe used. For instance, the coloring material in the ink may be acolloidal suspension in which case only the coloring particles will bedrawn through the sheet or the coloring material may comprise a dyewhich is dissolved in the liquid in which case the entire ink must besusceptible to electrostatic attraction.

Refer next to FIG. 2 wherein is shown a preferred embodiment of thenovel subject electrostatic printer. In the following description ofFIG. 2, as in the case of FIG. 1, numerous rollers are shown which aresuspended in suitable bearing means and driven by suitable rotatingmeans neither of which are shown, but which are obvious ly necessary. InFIG. 2 the thin endless insulator belt 1 having a plurality of holes 9passing therethrough is mounted on rollers 12, 8, 13, 14 and 15.Disposed adjacent the upperside of endless belt 1 is a latent imageforming means 3 which comprises a head member 16 having a plurality ofelectrostatic pins or probes 17 disposed in a line transverse to themovement of belt 1 as indicated by arrow 2. The pins 17 of the latentimage forming means 3 are in charging association with the insulatingbelt 1 such that when a DC. potential is selectively applied thereto, alatent image may be formed on the upper surface of the belt 1. Thelatent image forming means 3 is connected along line 18 to an imageformation control unit 19 which is connected along-line 20 to one sideof a direct current voltage supply 21. The other side of the directcurrent voltage supply is connected to line 22 which in turn isconnected to lines 23 and 24. Line 23 is connected to the conductor barwhich is disposed in the lower portion of an ink chamber 26 while line24 is connected to a corona discharge unit 27.

The image formation control unit 19 is a control unit for controllingthe selective application of pulses to the pins 17 of the latent imageforming means 3. Any of many well known types of image formation controlunits 19 can be utilized to perform this function. The image formationcontrol unit in turn accepts an input from a computer or other similarassociated master control unit.

The conductor probe or bar 25 extends the length of the ink chamber 26which in turn extends across the full Width of the insulator belt 1. Anink roller 28 is mounted for rotation and held by the ends of the inkchamber 26. An electrostatically attractable ink 29 is contained in theink chamber 26. Conductor bar 25 is in conductive association with theelectrostatically attractable ink 29 contained in the ink chamber 26.The roller 28 is held by the ends of ink chamber 26 such that it is inrolling contact with the lower surface of belt 1 and in contact with theink 29 held in the ink chamber 26.

The corona discharge unit 27 is a conventional commercially availablecorona discharge unit which functions to uniformly charge the surface ofinsulator belt 1 adjacent thereto as the belt is driven past it.

Rollers 13, 14 and 15 define a belt path which passes down into cleanerchamber 30 which contains a liquid cleaning agent 31. The belt ispinched between a cleaning blade or portion 32 and a pinch roller 33which functions to clean any excess cleaning liquid from the belt 1 asit leaves the cleaning unit. Roller 14 is mounted for rotation and heldby the ends of the cleaner chamber 30.

As in FIG. 1, a paper or print web 5 is brought in contact with theupper surface of the insulator belt 1 by means of roller 7.

In operation, as the endless thin porous insulator belt 1 moves in thedirection indicated by arrow 2 and the paper print web 5 moves in thedirection as indicated by arrow 6, a latent electrostatic image 10 isformed on the upper surface of belt 1 through selective energization ofthe electrostatic pins or probes 17 disposed in a line transverse to themovement of the belt 1. Energization of the electrostatic pins or probes17 of the head member 16 is under control of the image formation controlunit which receives an input from a computer or other associated mastercon trol unit (not shown). The image formation control unit 19, whichcontrols the selective energization of the pins 17, selectively appliesa direct current of a first polarity provided by the direct currentvoltage supply 21 to the pins 17. The latent image 10 then is moved pastthe polarized ink applicator 4 which contains ink 29 which is polarizedby means of the conductor bar 25 which is connected to the opposite sideof the direct current voltage supply 21. Thus, electrostaticallyattractable ink of an opposite polarity is applied to the lower surfaceof insulator belt 1. As the belt 1 moves toward the contact stationcomprising roller 7, the ink is pulled through the holes 9 in the belt 1by the latent image 10 to form an ink image 11. In those areas where thelatent electrostatic image 10 is not present, the ink is not pulledthrough the holes 9. The ink image 11 then passes in rolling contactwith the paper or print web 5 and is thereby transferred to the paperprint web. a

The insulator belt 1 containing the remanents of the ink image 11 andthe portions of ink 29 applied to the underside thereto which were nottransferred to the paper print web 5 then passes down through the liquidcleaning agent 31 contained in the'cleaner chamber 30. The ink remainingon the belt 1 is removed in the cleaner chamber 30. While only onecleaner chamber 30 and cleaning liquid 31 has been illustrated, it isobvious that any number of baths can be provided to assure adequate orthorough cleaning of the ink 29 from the insulator belt 1. The belt thenpasses between the cleaning blade 32 and pinch roller 33 which removethe fluid 31 from the belt.

While a fast drying cleaning agent 31 may be utilized such that theinsulator belt 1 is completely dry by the time that it reaches thecharging and inking station, it is obvious that additional drying meanssuch as a heater, air movement mechanism or vacuum cleaner, may beprovided.

The corona discharge unit 27 is not necessary for satisfactory operationof the system. It has been found, however, that if the upper portion ofthe insulator belt 1 is precharged to a polarity opposite to thatapplied by the pins 17 of the head member 16, that increased or higherresolution images will result.

While, in the heretofore described system, the electrostatic image hasbeen applied directly to the insulator belt 1, it will be obvious tothose skilled in the art that if the paper 5 had insulating propertiesthat the electrostatic image could be applied to the side of the paperwhich contacts the insulator belt. In such an application, as isobvious, the duration of contact between the insulator belt and paperwould have to be long enough to permit the electrostatic image to drawthe ink through the insulator belt.

In summary, an electrostatic printer is described in which the inputinformation forms a latent image 10 on the upper surface of an endlessbelt 1 made of thin insulating plastic material such as Teflon. The belt1 is perforated with many small, closely spaced holes 9. An inkingroller 28 applies electrostatically attractable ink 29 to the undersurface of the porous belt 1. A latent electrostatic image 10 is formedon the upper surface of the belt 1 by means of a high DC. potentialselectively applied across charging probes 17 and the inking roller 28beneath the belt 1. This charging station may 75 be replaced with anelectrostatic image transfer station.

Since the belt 1 contains numerous small holes 9, the polarizedmolecules of ink 29 on the under surface are attracted by charges ofopposite sign forming the latent image on the upper surface of thebelt 1. Consequently, ink 29 will be pulled upward through the holes 9in accordance with the charge pattern of the latent electrostatic image10. By the time the belt 1 reaches the print station comprising roller7, sufiicient ink 29 will have been pulled up through the holes 9 sothat ink characters can be transferred to a paper web 5 which is broughtinto contact with the upper surface of the belt 1.

In the above described manner, I have provided a novel electrostaticprinting means which employs a liquid developer to thereby eliminatehandling and fixing problems associated with the use of powderdevelopers. Additionally, one of the problems associated with prior artelectrostatic printers utilizing probe electrostatic heads to pull inkfrom an associated roller onto a paper or print medium has been overcomesince in the herein described system the timewise separation of theimage forming-inking step and the contactprinting step allows sufficienttime for the electrostatic ink to respond to the latent image pattern toprovide relatively high operational speeds.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in the form and detailsmay be made therein without departing from the spirit and scope of theinvention.

What is claimed is: 1. An electrostatic printer comprising: a thin,porous insulator belt of non-wettable material,

means for applying polarized ink to one side of said insulator belt,

means for causing said polarized ink to be selectively drawn throughsaid insulator belt to the other side thereof,

a print member, and

means for bringing said print member in printing contact with said otherside of said insulator belt.

2. An electrostatic printer comprising:

a thin, porous insulator belt of non-wettable material,

means for applying polarized ink to one side of said insulator belt,

means for applying an electrostatic image to the other side of saidinsulator belt to cause said polarized ink to be selectively drawntherethrough,

a print member, and

means for bringing said print member in printing contact with said otherside of said insulator belt.

3. An electrostatic printer comprising:

a thin, porous insulator belt of non-wettable material,

a latent image forming means disposed in operable association with afirst surface of said insulator belt,

a polarized ink applicator means disposed in operable association withthe other surface of said insulator belt, and

means for bringing a print member in printing contact with said firstsurface.

4. An electrostatic printer for printing on a print mem-' diumcomprising:

a thin, porous insulator belt of non-wettable material,

first and second roller members operable to cause said print member tobe brought into contact with a first surface of said insulator belt,

a latent image forming means comprising a plurality of selectivelyenergizable electrostatic probes disposed in operable association withsaid first surface of said insulator belt, and

a polarized ink applicator means disposed in operable association withthe other surface of said insulator belt.

7. An electrostatic printer for printing on an insulating I print mediumhaving an electrostatic image thereon comprising:'

a thin, porous insulator belt of non-wettable material,

first and second roller-members operable to cause said electrostaticimage to be brought into contact with a first surface of said insulatorbelt, and

a polarized ink applicator means disposed in operable association withthe other surface of said insulator belt.

8. An electrostatic printer for printing on a print member comprising:

a thin, endless, porous insulator belt of non-wettable material,

a latent image forming means including a plurality of selectivelyenergizable electrostatic probes disposed adjacent a first side of saidinsulator belt,

an image formation control unit electrically connected to said latentimage forming means for applying a direct current of a first polarity tosaid selectively energizable electrostatic probes,

a polarized ink applicator disposed on the opposite side of saidinsulator belt comprising an ink roller in rolling contact with saidopposite side of said insulator belt electrically connected to a directcurrent potential of opposite polarity,

first and second rollers operable to cause said print member to bebrought into contact with said first surface of said insulator belt,

cleaning means in operable association with said insulator belt, and

means for moving said insulator belt in a direction such that a givenportion of said insulator belt passes in sequence past said latent imageforming means and said polarized ink applicator means, between saidfirst and second rollers, and through said cleaning means.

9. An electrostatic printer for printing on a print member comprising:

a thin, endless, porous insulator belt of non-wettable material,

a latent image forming means including a plurality of selectivelyenergizable electrostatic probes disposed adjacent a first side of saidinsulator belt,

an image formation control unit electrically connected to said latentimage forming means for applying a direct current of a first polarity tosaid selectively energizable electrostatic probes,

a polarized ink applicator disposed on the opposite side of saidinsulator belt comprising an ink roller in rolling contact with saidopposite side of said insulator belt electrically connected to a directcurrent potential of opposite polarity,

first and second rollers operable to cause said print 3,096,198 7/1963Schaifert 118-637 X member to be brought into contact with said first3,102,045 8/1963 Metcalfe et al. 117-37 surface of said insulator belt,cleaning means in operable association with said insu- References C1195by the PP lator g; h b1 6 UNTTED STATES PATENTS a corona isc arge unit1n opera e association wit said first side of said insulator belt, andggg z means for moving said insulator belt in a direction 25589OO 7/1951H p such that a given portion of said insulator belt 2558901 M1951passes in sequence past said latent image forming 1o 2583375 1/1952 YTmeans and said polarized ink applicator means, be- 4/1953 555 tween saidfirst and second rollers, through said 8/1956 8 cleaning means, and pastsaid corona discharge unit. 2758525 8/1956 figgg ggl References Cited bythe Examiner 15 2932548 4/1960 Nam 2,932,690 4/1960 Adams, UNITED STATESPATENTS 2,777,745 1/1957 McNaney 117 17-5 X CHARLES A. WILLMUTH, PrimaryExammcr. 2,832,511 4/1958 Stockdale et al. '118-637 X WILLIAM MARTIN3,045,644 7/1962 Schwertz 118-637 X 20 PETER FELDMAN, AssistantExaminer.

1. AN ELECTROSTATIC PRINTER COMPRISING: A THIN, POROUS INSULATOR BELT OFNON-WETTABLE MATERIAL, MEANS FOR APPLYING POLARIZED INK TO ONE SIDE OFSAID INSULATOR BELT, MEANS FOR CAUSING SAID POLARIZED INK TO BESELECTIVELY DRAWN THROUGH SAID INSULATOR BELT TO THE OTHER SIDE THEREOF,A PRINT MEMBER, AND MEANS FOR BRINGING SAID PRINT MEMBER IN PRINTINGCONTACT WITH SAID OTHER SIDE OF SAID INSULATOR BELT.